I propose a combined experimental-theoretical approach to (1) study pulsatile pulmonary hemodynamics on-line under a variety of physiological and pathological conditions and (2) to improve and correlate two existing methods of investigation in hemodynamics. The long-term objective of this project is two-fold: (1) scientifically, to understand the behavior of the pulmonary vasculature under pulsatile flow conditions and to limit the body of information which has been obtained with steady flow to the results from the pulsatile flow experiments; (2) practically, to establish distinct patterns of the impedance spectra under different conditions and use such information as a means of online evaluation of the state of pulmonary hemodynamics. Experiments will be performed in dogs with two basic preparations: (1) intact right heart and cannulated left lung, either open chest or closed chest; (2) isolated left lower lobe, either in situ or in vitro, perfused by a pulsatile pump. In the first preparation instantaneous pressure-flow relationships will be recorded accurately and pulmonary vascular input impedance will be computed on-line. In the second preparation, arterial and venous occlusion (AVO) will be applied with precision and input impedance measurements will also be made. These data will be analyzed both on-line and off-line. Since the AVO technique elicits the impulse responses of the vascular system in the time-domain and input impedance characterizes the vascular system in the frequency-domain, an attempt will be made to correlate the results obtained from these two methods. In the intact right heart experiments, the pressure-flow relationship during the brief period when the pulmonary vascular bed discharges passively will be examined in particular. The effect of the left atrium on the pulsatility in the entire pulmonary vascular bed will also be investigated. The pathophysiological conditions to be studied in this project include lung inflation, hypoxia, effects on serotonin, isoproterenol and norepinephrine infusion, hemodilution, pulmonary embolism, acute lung injury with permeability edema, hydrostatic edema, endotoxic shock, hemorrhagic shock, and effects of IPPB ventilation and PEEP.